Chief among female mortality is the development, progression, and metastasis of aggressive breast cancer. The bidirectional communication between the neoplastic cells and the tumor microenvironment, which supplies oxygen and nutrients, is essential for promoting unchecked tumorigenic development, aberrant neovascularization, and widespread metastasis. Thus, a better understanding of embedded cues and soluble messages exchanged between these two compartments will prove invaluable for furthering our knowledge of the pathobiology of cancer and for reliably predicting clinical outcomes. Our central hypothesis is that endorepellin, a proteolytic fragment of perlecan, a multi-domain heparan sulfate proteoglycan, exploits a dual-receptor antagonism to preclude endothelial cells from participating in tumor angiogenesis. This working hypothesis is based on an impactful and promising body of work all generated under the auspices of this grant. We discovered that: [a] Endorepellin simultaneously ligates, with high affinity, VEGFR2 and the ?2?1 integrin thereby constituting the molecular basis of ?dual receptor antagonism?. Engagement of both receptors underscores the exquisite sensitivity and specificity of endorepellin in targeting the endothelia. [b] Endorepellin triggers co-internalization of VEGFR2 and ?2?1 integrin with concurrent activation of the SHP-1 tyrosine phosphatase and attenuation of VEGFA signaling. [c] Endorepellin induces endothelial cell autophagy in a Peg3-dependent manner by modulating Beclin 1, LC3, and p62 expression, processing, and cellular localization. [d] Endorepellin evokes protracted activation of the energy-sensor kinase AMPK?, irrespective of energy levels. Indeed, this regulation is considered non-canonical as AMPK? phosphorylation occurred under nutrient-enriched conditions. [e] Downstream of AMPK?, endorepellin evokes autophagic flux in endothelial cells that mechanistically parallels the mTOR inhibitor, Torin 1. These striking findings demonstrate that protracted and sustained autophagy is a novel mechanism by which endorepellin promotes angiostasis, independent of nutrient deprivation. Based on these discoveries, we plan to: [1] Elucidate the mechanism of endorepellin-evoked endothelial cell stress, autophagy and mitophagy. [2] Unravel the mechanism by which endorepellin induces autophagic suppression of HAS2. [3] Generate novel mouse models of tumorigenesis to explain the pro-autophagic and anti-angiogenic programs activated by endorepellin. These concerted research aims will enable us to translate our findings, procured with highly innovative mouse models of stromal autophagy, into clinically relevant paradigms. The discovery of endorepellin-induced endothelial cell autophagy downstream of dual receptor antagonism will lead to new therapeutic advances that actively induce autophagy within the tumor microenvironment to combat this devastating disease.